ITMI971206A1 - PROCEDURE FOR THE PURIFICATION OF LANDFILL PERCOLATE USING ULTRAFILTRATION AND REVERSE OSMOSIS - Google Patents

Description

Patent application for industrial invention entitled:

"Process of purification of landfill leachate by ultrafiltration and reverse osmosis"

1. Field of the invention

The present invention relates to a multistage physical process for the treatment of landfill leachate, based on ultrafiltration and reverse osmosis.

Landfill leachate is a particularly polluting sewage, which is formed in landfills of municipal solid waste.

Reverse osmosis is a separation technique that is based on applying a pressure to the liquid to be purified to overcome the osmotic pressure, forcing pure water to permeate through a semipermeable membrane, with the production of a purified liquid phase (permeate ) and a concentrated liquid residue in which the organic and inorganic impurities contained in the leachate are found.

Ultrafiltration aims to pre-treat landfill sewage, removing suspended solids, soluble colloidal and organic fractions with high molecular weight, to make it suitable for subsequent reverse osmosis treatments.

This procedure allows to reduce the environmental impact of landfill leachate, concentrating the pollutants in a reduced volume, in order to make subsequent disposal outside the landfill economical, while most of the starting leachate deprived of polluting species ( permeate), can be disposed of in surface water courses (rivers, etc.), being made suitable for discharge, in compliance with the more restrictive limits of acceptability of Table A of the Italian law 319/76 and European regulations.

2. State of the art

Typical processes for the purification of contaminated water include an ultrafiltration stage to reduce biological, particulate and colloidal contaminants, and two stages of reverse osmosis ("ACWA builds leachate treatment plant", Industriai News, Nov. 1993. P- 59) ·

The purification of landfill sewage by reverse osmosis presents various problems: in fact they contain considerable quantities of organic substances, often difficult to eliminate even with ultrafiltration pre-treatments; they also contain substances in a colloidal state, with a gelatinous consistency, which tend to occlude the pores of the filtering membranes, reducing their separation efficiency, and making frequent washing of the membranes necessary, with a decrease in their average life and an increase in operating costs; moreover, they contain quite considerable quantities of ammonia, deriving from the putrefaction processes of organic materials, which with traditional procedures is found in the final permeate in quantities often higher than the values allowed by law, and whose elimination requires further pre-treatments, often onerous from an economic point of view, such as the passage in special stripping towers ("ACWA builds leachate treatment plant", Industriai News, Nov. 1993. P- 59) ·

Furthermore, the total salinity of the leachate is so high that as the liquid to be purified is concentrated in the osmosis unit and the aqueous phase is continuously removed, the osmotic pressure reaches values so high as to affect the efficiency and efficiency of the separation.

According to the known art, each reverse osmosis stage is carried out at constant operating pressure. According to U. Theilen, Process Comhination, Trade Related Articles, in Chemical Plants and Processing, November, 1994, p. 12-14, some stages of reverse osmosis at 30-50 bar can be followed by some stages conducted at a pressure between 120 and 200 bar, to further concentrate the liquid: by carrying out a whole stage of osmosis at high pressure, however, it increases considerably the energy and therefore economic expenditure of the purification process.

The need is therefore felt to have available new processes for the purification of landfill leachate, effective, economical, suitable for realization on an industrial scale, which overcome the drawbacks of the known art.

2 . Summary

The Applicant has found a multi-stage process for the purification of a landfill leachate, comprising

a) an ultrafiltration stage;

b) one or more reverse osmosis stages (preferably 2),

characterized in that at least one reverse osmosis stage, preferably the first, is carried out by realizing at least one pressure increase in the circuit of the liquid circulating under pressure in a single osmosis unit (i.e. in a single osmosis stage). This increase is achieved by inserting in series in the circuit of the liquid circulating in a given osmosis unit at least one auxiliary pump PB (booster pump, or "booster" pump), which produces an increase in pressure of the liquid circulating in a given osmosis unit at a pressure higher than atmospheric (thanks to the high pressure pump), without interrupting the circuit in any way.

The auxiliary pump therefore allows to work at at least two different operating pressures in the same osmosis stage, at a lower pressure in a previous stage, and at a higher pressure in the stage following insertion of the pump.

The present leachate purification process is further characterized in that the ultrafiltration step is preferably carried out at a temperature of at least 30 ° C, more preferably between about 30 ° C and 50 ° C.

The upper limit of ultrafiltration temperature is dictated by the limit of economic convenience, and depending on the case it can also be higher than the limit indicated above.

Furthermore, further objects of the present invention constitute:

a plant for the treatment of landfill leachate comprising an ultrafiltration section and one or more osmosis sections, characterized in that it comprises at least one auxiliary pump inserted in series in the circuit of a single osmosis unit, said pump being in particular interposed between two successive groups of osmosis membranes, forming part of the same osmosis unit, so as to achieve an increase in the pressure of the fluid circulating under pressure (ie at a pressure higher than the atmospheric one) in said osmosis unit;

- a plant for the treatment of landfill leachate - comprising an ultrafiltration section and one or more osmosis sections, characterized in that it comprises a device for heating the leachate placed before the ultrafiltration membranes.

3 · Brief description of the Figures

Figure 1 represents the block diagram of a plant for the purification of landfill leachate according to the present invention.

Figure 2 represents the block diagram of a reverse osmosis section according to the present invention, comprising 4 "loops" of osmosis membranes.

Figure 3 illustrates the cross section of an ultrafiltration ceramic membrane element.

Figure 4 illustrates a reverse osmosis membrane element with a spiral configuration.

3 · Detailed description

The present process is described below in greater detail, with reference to the Figures.

In the present text, by osmosis unit we mean the apparatus comprising a grouping of membranes in which a stage of osmosis is conducted, from the introduction of the liquid to be treated previously brought to the operating pressure selected by means of a special pump, up to the discharge of the permeate, at atmospheric pressure.

In the first stage of reverse osmosis of the present process, the operating pressure is preferably between about 30 and 120 bar, (for example ≥ 30 bar and <120 bar), meaning in the present text the operating pressure imposed on the fluid to be treated. , to overcome the osmotic pressure.

Typically, for the purposes of the present invention, each reverse osmosis section (unit) contains several groups of osmosis membranes ("loops") (typically from 2 to 6), each in turn containing one or more pressure vessels ("pressure vessels "), for example in number from 2 to 6, placed in series and / or in parallel within each" loop ": each pressure vessel in turn contains two or more individual osmosis membranes (preferably spiral cartridges ), for example from 2 to 6, placed in series inside it. Each L1-L4 "loop" is powered by a PR1-PR4 recirculation pump, which continuously recirculates the liquid to be filtered inside.

To increase the operating pressure in the preselected osmosis stage, preferably in the first, a single PB auxiliary pump is generally sufficient.

In practice, an auxiliary PB pump takes the concentrate Cx at the outlet from a group of osmosis membranes, and sends it at an increased pressure to the next group of membranes in the same osmosis unit, thus allowing to work at two different operating pressures in the same osmosis unit. osmosis stage, ie at a lower pressure in a group of membranes or "loops", and at a higher pressure in the subsequent "loops" of the same osmosis unit. According to a particular embodiment of the present invention, the auxiliary pump is inserted in series between a first series and a second series of membrane groups ("loops") of the same osmosis unit, each series being for example constituted by two " loops "(Figure 2).

Preferably, one operates at pressures between about 30 and 50 bar upstream of the auxiliary pump (in particular in the first series of "loops"), and at pressures between about 50 and 120 bar

(for example> 50 and <120 bar) downstream of the auxiliary pump (in

particularly in the second series of "loops").

The use of the auxiliary pump according to the present invention

allows to overcome the osmotic pressure increase and the

consequent reduction of the difference between applied pressure and

osmotic pressure, which is found as osmosis proceeds for

the continuous removal of Px permeate and the progressive

concentration of the liquid to be purified, and which determines

slowdown of the flow and decrease in yield

osmosis; moreover, it allows you to work optimally, eg

an early operating pressure lower than it would be

necessary to apply working at constant pressure to maintain

an equal performance, revealing itself in particular extremely

advantageous with respect to the methods of the prior art

remember, they use reverse osmosis stages entirely

ducts at constant operating pressures between 120 and 200

bar. The use of lower operating pressures allows to preserve the life of the osmosis membranes for longer, reduces the

energy consumption and therefore operating costs.

Preferably, one or more of the membrane separation steps

of the present procedure, preferably all, both those of

ultrafiltration that those of reverse osmosis are carried out

by cross-flow filtration, pumping the liquid to be treated

according to a flow parallel to the filtering surface.

While the liquid flows parallel to the filter surface, the filtrate is continuously removed.

This parallel flow generates a high turbulence, which prevents the particles suspended in the liquid from settling on the pores of the surface of the filtering membrane, thus avoiding its rapid clogging, and thus allowing to maintain stable filtration yields for long periods. The flow velocity of the liquid, called the tangential velocity, is a very important operational parameter, which controls the efficiency of the tangential filtration (quantity of liquid removed as filtered or permeated Px in the unit of time).

In particular, for the ultrafiltration process the higher the tangential velocity, the higher this yield. In the present process, in ultrafiltration cross-flow filtration rates are used preferably between 3 and 6 meters / second.

When significant soiling of the membranes occurs, the restoration of the flows to optimal values can be obtained with various washing techniques, including backwashing.

Before being subjected to the ultrafiltration and preheating steps according to the present invention, the leachate arriving from the landfill is typically subjected to one or more conventional pre-treatments, such as homogenization, biological nitrification-denitrification; clarification by filtration on conventional sieves for the separation of particulate and coarse material, to make it suitable for subsequent treatments.

According to a particular embodiment of the present invention, the leachate to be subjected to ultrafiltration is stored in an accumulation tank V (Figure 1), at a temperature generally of about 5 ° C / + 20 ° C, and, before sent to the ultrafiltration section, it is pre-heated to the temperature selected for ultrafiltration according to the present process.

The leachate is for example pre-heated by passing through a heat exchanger illustrated in Figure 1), placed before the ultrafiltration section, (for example between the boiler C and the tank SI, or in the tank SI), and therefore in general stored in an S1 tank. The heating fluid of the exchanger is produced by a boiler C, fed by any energy source (methane, landfill gas, etc.).

According to a typical embodiment of the present invention, the leachate stored in the accumulation tank - through the heat exchanger is sent to the ultrafiltration system UF by means of a PAUf feed pump, at a flow for example of about 5 cubic meters / hour ( mc / h), and then continuously circulated inside the membrane modules of the UF ultrafiltration unit by means of a high flow PRUf recirculation pump.

The linear speed of circulation of the liquid in the ultrafiltration section UF is preferably about 3-6 m / second. The fact of carrying out the ultrafiltration according to the present process at a temperature of at least 30 ° C, is advantageous above all for the ultrafiltration, which proceeds with higher yields with the same filtering surface than the processes that operate at lower temperatures, for example at about 5 ° C / + 20 ° C, allowing a higher concentration of pollutants, allowing to decrease the frequency of washing of the ultrafiltration and reverse osmosis membranes, and reducing operating costs.

Furthermore, the fact of carrying out the ultrafiltration at at least 30 ° C has also proved to be advantageous for the yields and efficiency of the subsequent reverse osmosis stages. In particular, it allows them to be carried out at a preferred temperature of at least 25 ° C (for example about 25 ° C / + 30 ° C), which, according to an advantageous embodiment of the present process, is obtained by cooling the permeate coming from the ultrafiltration. in a heat exchanger that uses the same starting leachate as the cooling fluid (that is, the one stored at 5 ° / + 20 ° C in the storage tank).

Furthermore, it has been observed that at about 25 ° C / + 30 ° C, reverse osmosis works with greater permeation efficiency at the same pressure, allowing the use of preferred operating pressures of about 30-120 bar, on average lower than traditionally. used, with a consequent reduction in wear and frequency of replacement of the mechanical structures and membranes of the plants, and therefore with savings in operating costs. The leachate to be ultrafiltered and the ultrafiltered Px permeate have a generally alkaline pH, generally comprised between 7.5 and 8.8.

In the present process, the ultrafiltration membranes are preferably ceramic membranes, comprising a support of α-Αl Ο3 coated with an active layer of ZrO.

For the purposes of the present invention, ultrafiltration membranes with a multichannel tubular configuration are further preferred.

An example of an ultrafiltration membrane useful for the purposes of the present invention is the membrane Me illustrated in Figure 3, comprising a support Sp of α-Αl Ο3 with a hexagonal section, in which various channels Ch are obtained, the internal surface of which, intended for contact with the liquid to be treated, is coated with a layer of ZrO. Examples of ultrafiltration ceramic membranes useful for the present invention are marketed under the name of MEMBRALOX by S.C.T. (Société Céramique Francais, of the US Filter).

In Figure 3. the arrow, parallel to the length of the canaliculi Ch, indicates the direction of entry of the fluid Fx to be ultrafiltered; the arrow P2, parallel to the direction P1, the outlet of the waste liquid (concentrated, Cx), and the arrow P3, perpendicular to P1, the outlet of the ultrafiltered liquid (permeate Px): in each of these ultrafiltration membranes , the (concentrated) waste liquid Cx, collected in the outlet direction P2, is recirculated several times at high speed along the filter channels by means of the aforementioned recirculation pump.

In the present UF ultrafiltration unit there are typically several ultrafiltration membranes, grouped into modules: each module contains several membranes, and the various modules are in turn grouped in series and / or in parallel in groups of membranes, called "loops", for example in number from 2 to 5: each "loop" is fed by a high flow recirculation pump. According to a further preferred feature of the present process, ultrafiltration membranes are used with porosity between about 5 and 100 nanometers (nm), more preferably about 50 nm, associated with transmembrane pressures preferably between 0.5 and 3.5 bar , in relation to the specific porosity adopted, where the transmembrane pressure is defined as follows:

where, Prp is the transmembrane pressure, and with reference to Figure 3, is the pressure exerted by the fluid Fx entering each ultrafiltration module; P2 is the pressure of the concentrate Cx (waste phase) leaving the ultrafiltration module; P3 the pressure of the permeate Px leaving the ultrafiltration module.

At the beginning of the ultrafiltration there are quite low transmembrane pressure values, for example of about 0.5-0.8 bar; then, as the ultrafiltration proceeds and the filter system tends to become saturated due to the presence of particulate and colloidal material, the pressure tends to rise, up to about 3-5 - The use of ceramic membranes with porosity of 5 "100 nm at transmembrane pressures of 0.5-3t5 bar allows to obtain specific filtration flows higher than the previously known processes, which use membranes with porosity higher than 100 nm, in particular of about 0.2 micrometers {about 200 nm) , associated with transmembrane pressures of 0.5-1.5 bar. In the present process, the transmembrane pressure values are conveniently controlled within the preferred values indicated above, by adjusting the opening and closing of the permeate outlet valve Px and of the concentrate outlet valve Cx (not shown in the Figures), to obtain a flow rate as constant as possible, also convenient for feeding the subsequent stages. The flows of concentrate Cx and permeate Px leaving the ultrafiltration step according to the present process are for example respectively regulated to values of about 0.15 mc / h and about 4.85 mc / h.

The ultrafiltration carried out at at least 30 ° C (in particular preceded by pre-heating) according to the present process entails significant advantages, which are also reflected in the subsequent reverse osmosis steps. In particular :

- it allows to preserve the ultrafiltration membranes from fouling for longer than the previously known processes, avoiding numerous chemical washes, and therefore increasing their average life, which in the present case can even reach several years, as extrapolated from the experimental wear data so far obtained; - it allows to push the volumetric concentration of the waste effluent up to otherwise impossible levels, under penalty of severe fouling of the membranes with regeneration difficulties;

- the use of ultrafiltration membranes with reduced porosity with respect to the previously known techniques associated with on average higher transmembrane pressures, allows to obtain higher filtration flows;

- allows the use of spiral membranes for reverse osmosis (as illustrated below), which are more advantageous, both from an energy point of view (low installed power) and operating costs (costs of replacement membranes, ease and speed of interventions for the replacement, reduced dimensions); - it allows the easy and rapid washing of the reverse osmosis membranes, with intervals between one cycle and the next widely spaced over time;

- allows a longer average life of osmosis membranes. The permeate Px leaving the ultrafiltration stage is typically characterized by: a "fouling" index SDÌ <5 (SDÌ = Silt Density Index = Dirty Index), and a turbidity index NTU <1 (NTU = Nephelometric Turbidimetric Unit = Nephelometric Turbidity Unit).

The concentrate Cx leaving the ultrafiltration stage is disposed of, while the permeate Px passes to the subsequent reverse osmosis phases.

The reverse osmosis steps of the present process are preferably carried out at a temperature of at least about 25 ° C, more preferably at about 25 ° C / + 30 ° C.

In the present invention, the permeate Px leaving the ultrafiltration unit UF is preferably sent through a heat exchanger fed by the initial leachate having a temperature of 5 ° / + 20 ° C, which allows the permeate to be brought to a temperature of 25 ° C / + 30 ° C, to an S2 tank. from which it is then sent to the first osmosis section 01-1.

The heat released through the exchanger is conveniently recovered to feed the aforementioned preheating phase. According to a further preferred characteristic of the present process, before being subjected to reverse osmosis, the ultrafiltered permeate Px, which as reported above has an alkaline pH, is acidified, to a pH preferably between 5.0 and 6.5. more preferably between 5.5 and 6.0.

Acidification is typically carried out by adding an inorganic acid, such as hydrochloric or sulfuric acid.

Generally, the acidification device is placed inside the first osmosis unit, before the pump feeding the osmosis membranes.

The acidification according to the present procedure allows the quantity of NH3 of the final permeate Px to be effectively controlled within levels admissible by law.

Apart from the aforementioned acidification treatment, before being subjected to osmosis, the ultrafiltered permeate Px is also typically subjected to one or more conventional pre-treatments, for example with anti-scaling agents and / or with sterilizing chemical agents.

The osmosis membranes preferably used in the present process, in particular in the first osmosis stage, are those with a high salt rejection, in particular equal to at least 95%, more particularly with a high NaCl rejection (for example a rejection of NaCl about 98.8% -99%)

The saline rejection expresses the% of a salt, in this case NaCl, which is retained in the concentrate by an osmosis membrane, under the following operating conditions: aqueous solution containing 32,000 mg / liter of NaCl; working pressure of 800 psig - (5-516 KPa), at 25 ° C, pH 6.5; % recovery equal to 13%, after 24 hours. The flow in the individual osmosis elements can vary around ± 15%.

Unlike the membranes commonly used and marketed for the desalination of sea water, which can be used up to a maximum pressure of 70-80 bar, those with high saline rejection can reach operating pressures up to 120 bar, avoiding the phenomena of compaction common to standard membranes, and also allowing high rejections (from the permeate) of both organic compounds and ammonia.

For the purposes of the present invention, reverse osmosis membranes with a spiral configuration are further preferred, such as for example the membrane Mo shown in Figure 4, for example those marketed by DESAL Membrane Products, having for example a diameter of 4 "or 8" (inches) and length, for example about 40 '' (inches), or the membranes marketed by FILMTEC.

In the present process, the feeding of the permeate Px to the osmosis units (both the first and the second) typically occurs by means of a feed pump PA1 and a high pressure pump PA2 (Figure 2).

The permeate Px leaving each loop of the first osmosis unit 01-1 is gradually collected with that of the subsequent "loops", and sent to the next stage, in particular to the second osmosis section 01-2 (Figure 2).

By way of example, as illustrated in Figure 2, the first osmosis section can contain 4 "loops" L1-L4, connected together in series, each fed by its own PR1-PR4 recirculation pump; each "loop" in turn contains 3 pressure vessels, arranged in series and / or parallel within the "loop", each of which contains 3 cartridges of spiral membranes (not shown in Figure 2).

Preferably, the fraction of permeate Px leaving the last "loop" of the first osmosis section 01-1 is recycled at the head of the first "loop" and reprocessed, obtaining a further quality increase of the permeate Px.

Typically, in the present process, the concentrate Cx leaving the first osmosis section 01-1 is discarded and sent for disposal, together with that produced by ultrafiltration. The permeate Px obtained from the first reverse osmosis stage 01-1 is typically sent to a tank S3, from which it is then sent to the second osmosis section 01-2 (Figure 1). The flows of concentrate Cx and permeate Px leaving the first osmosis unit are for example regulated around 0.6 mc / h and 4.65 mc / h respectively.

The second osmosis stage of the present process can be realized various types of known membranes, at operating pressures preferably comprised between about 40 and about 70 bar, more preferably applying a constant operating pressure. In fact, in the second stage of reverse osmosis it is generally not necessary to increase the pressure, since the permeate Px produced in the first stage has a rather high level of purification, and the second stage has the function of perfecting this purification.

Purely by way of example, the second osmosis unit 01-2 can consist of 3 "loops", each containing 2 pressure vessels, each of which in turn contains 3 spiral membrane cartridges.

In the present process, the concentrate Cx leaving the second reverse osmosis stage is typically recycled to the first stage 01-1 (Figure 1), and the permeate Px leaving the second reverse osmosis unit 01-2 to a tank S4, to be which is then sent to the drain.

This process, applied for example to a leachate with an initial conductivity of for example 15-000-20.000 pS / cm, allows to obtain recovery volumes of the final permeate Px on average 85 # compared to the initial volume of treated landfill leachate, and volumes of concentrate Cx to be disposed of typically 13% of the treated leachate, with a final volumetric concentration factor FCV equal to approximately 6 times the original volume of the treated liquid, where

wherein VE is the volume of liquid entering a separation stage and VC is the volume of concentrate Cx leaving the same stage.

The present process allows to obtain FCV having for example the following values, step by step: ultrafiltration FCV = 30; first stage of reverse osmosis FCV = 9; second stage of reverse osmosis FCV = 11.

This procedure is suitable for example for the treatment of landfill leachate containing NH4> 1200 ppm, with conductivity ≥ 10,000 pS / cm, allowing to obtain a permeate Px at the end of the process with values of ΝΗ4 ≤ 10 ppm and with conductivity <100 pS / cm (micro Siemens / cm).

The regulation of the inlet speed of the fluid to be treated and the outlet speed of concentrate Cx and permeate Px in the various stages of this process essentially responds to the need to have flows that are as constant as possible and functional to the needs of industrial production cycles, preferably in order to complete a leachate purification cycle in a single working day. The flows in mc / h reported above with reference to the various stages therefore have a purely illustrative value, as they can be varied within wide limits according to specific needs.

The selection of operating conditions according to the present process allows to achieve a purifying efficiency that is constant over time, even when the characteristics of the liquid entering the ultrafiltration vary. The ultrafiltration and reverse osmosis modules maintain high average filtration flows for a long time, and their regenerability is excellent.

The following example is given for illustrative but not limitative purposes of the present invention.

EXAMPLE 1

In an industrial plant similar to the one schematized in Figures 1 and 2, 60 to 240 meters / cubic meters per day are treated of a landfill leachate having the characteristics shown in Table 1, obtaining a permeate Px having the characteristics also shown in Table 1.

Characteristics of the plant

Leachate treatment capacity: 100 cubic meters / day

Installed power: 305 kW

Final permeate quality: within the limits of Table A of the Italian law 319/76

MEMBRALOX ultrafiltration ceramic membranes.

DESAL 4 '' spiral osmosis membranes.

Initial storage section - Leachate accumulation tank

t = 5 ° C / + 20 ° C; pH 7.5 - 8.8

Leachate feeding to the storage tank: 5 mc / h Preheating section

Heating at 30 ° C / + 50 ° C

Ultrafiltration section

2 loops, each containing four MEMBRALOX modules (parallel of two elements in series)

t = 30 ° C / 50 ° C; PH 7.5 - 8.8;

transmembrane pressure 0.5-3.5 bar;

concentrate Cx at the outlet: 0.15 mc / h; permeate outlet: 4.85 mc / h FCV = 30

Passage in heat exchanger

The temperature drops to 25 ° C / + 30 ° C, with heat recovery which is used to power the preheating phase.

Tank storage section

Reverse osmosis section. 1st stage

Four loops, each containing 3 pressure vessels, each in turn containing 3 DESAL cartridges of 4 '' x 40 '' t = 25 ° C / 30 ° G pH 5.5 - 6

P loop 1,2 = 30-50 bar; P loop 3.4 = 50 "120 bar; FCV = 9 concentrated output: 0.6 mc / h; outgoing permeate: 4.65 mc / h Storage section between the and 2nd osmosis unit

The permeate from the first osmosis unit is accumulated in an intermediate tank before feeding the next stage. Reverse osmosis section, 2nd stage

3 "loops" containing 2 pressure vessels, each containing 3 cartridges of membranes with high saline rejection,

t = 25 ° C / 30 ° C; pH 5 - 6; P = 40-70 bar; FCV = 11 concentrate at the outlet: 0.40 mc / h: permeate at the outlet: 4.25 mc / h The concentrate is recycled to the first reverse osmosis unit. The final permeate has a clear and colorless appearance, no odor is perceptible near the tank: it is collected in an accumulation basin, before being sent to the drain.

PARAMETER MINIMUM VALUES - MAXIMUM VALUES

PERCOLATED IN PERMEATED ENTRANCE

THE FINAL

T (° C) 5 - 30 -PH 6.0 - 8.5 6.0 - 6.5 Cond.

(pS / cm) 5200 - 20.000 <100 NH4-N ppm 295 - 1200 <10 TOC ppm 600 - 2000 <17 BOD ^ ppm 300 - 1200 <20 COD ppm - 1200 <15 TDS ppm 5000 - 10000 - AOX ppm 1.5 - ~ ≤ 0.04

Cond. = Conductivity;

NH4-N = ammonium nitrogen

TOC = Total Organic carbon COD = chemical oxygen demand;

BOD5 = biochemical oxygen demand after 5 days at 20 ° C TDS = Total Dissolved Solids AOX = Halogenated organic compounds

Claims (6)

CLAIMS A multi-stage process for the purification of a landfill leachate, comprising a) an ultrafiltration stage; b) one or more stages of reverse osmosis, characterized in that at least one reverse osmosis stage is carried out by realizing at least one pressure increase in the circuit of the liquid circulating under pressure in a single osmosis unit, said increase being obtained by inserting in series in said circuit at least one auxiliary pump PB. 2. Process according to claim 1, wherein the ultrafiltration step is carried out at a temperature of at least 30 ° C. 3. Process according to claim 2, wherein the ultrafiltration step is carried out at a temperature between 30 ° C and 50 ° C. 4. Process according to claim 1 or 2, in which the first reverse osmosis stage is carried out at an operating pressure comprised between 30 and 120 bar. 5. Process according to claim 1 or 2, in which in the first reverse osmosis stage one operates at pressures ranging from 30 to 50 bar upstream of the auxiliary pump PB, and at pressures ranging from 50 to 120 bar downstream of the auxiliary pump PB. 6. Process according to claim 1 or 2, wherein each section (unit) of reverse osmosis contains several groups of osmosis membranes ("loops") L 1, each in turn containing one or more pressure vessels placed in series and / or in parallel within each "loop": each pressure container in turn contains two or more individual osmosis membranes placed in series inside it; each L1-L4 "loop" is powered by a PR1-PR4 recirculation pump, which continuously recirculates the liquid to be filtered inside. 7- Process according to claim 6, wherein the auxiliary pump PB is inserted in series between a first series and a second series of groups of auxiliary membranes or "loops" 8. Process according to claim 1 or 2, in which one or more stages are carried out by cross-flow filtration, pumping the liquid to be treated according to a flow parallel to the filtering surface. 9- Process according to claim 8, in which the ultrafiltration stage is carried out at a tangential filtration rate of between 3 and 6 meters / second. 10. Process according to claim 2, in which the leachate is stored in an accumulation tank V, at a temperature of 5 ° C / + 20 ° C, and subjected to pre-heating by passing through a heat exchanger, and then stored in an S1 tank. 11. Process according to claim 1 or 2, in which the leachate stored in the accumulation tank V is sent to the ultrafiltration system by means of a feeding pump PAUf and is recirculated inside the membrane modules of the ultrafiltration section UF by means of a high flow PRUf recirculation pump. 12. Process according to claim 1 or 2, wherein the ultrafiltration membranes are ceramic membranes, comprising a support of α-Al O3 coated with an active layer of ZrO. 13. Process according to claim 12, wherein said membranes have a multichannel tubular configuration. 14. Process according to claim 1 or 2, in which several ultrafiltration membranes are placed in the ultrafiltration unit, grouped into modules: each module contains several membranes, and the various modules are in turn grouped in series and / or in parallel in groups of membranes, called "loops", each "loop" being fed by a high flow recirculation pump. 15. Process according to claim 1 or 2, in which ultrafiltration membranes with porosity between 5 and 100 nanometers are used, associated with transmembrane pressures PT between 0.5 and 3.5 bar, where where Prp is the transmembrane pressure, and with reference to Figure 3. P1 is the pressure exerted by the liquid entering the ultrafiltration section; P2 is the pressure of the concentrate Cx (waste phase) leaving the ultrafiltration section; the pressure of the permeate Px leaving the ultrafritration. 16. Process according to claim 15. wherein said porosity is 50 nm. 18. Process according to claim 1 or 2, in which the reverse osmosis stages are 2 and are carried out at at least 25 ° C. 19- Process according to claim 18, in which the reverse osmosis steps are carried out at a temperature comprised between 25 ° C and 30 ° C. 20. Process according to claim 19. wherein the permeate Px leaving the ultrafiltration unit UF is sent to a tank S2 through a heat exchanger, fed by the initial leachate having a temperature of 5 ° C / + 20 ° C, which allows the permeate to be brought to a temperature of 25 ° C / + 30 ° C, and from this tank it is then sent to the first osmosis section 01-1, the heat released through the exchanger being recovered to feed the aforementioned pre-heating phase . 21. Process according to claim 1 or 2, wherein the ultrafiltered Px permeate, before being subjected to reverse osmosis, is acidified to a pH of between 5.0 and 6.5-22. Process according to claim 21, wherein said pH is comprised between 5.5 and 6.0. 23- Process according to claim 1 or 2, in which reverse osmosis membranes with high NaCl rejection are used, equal to at least 95%, where the rejection expresses the percentage of NaCl retained in the concentrate by a membrane, under the following operating conditions : aqueous solution containing 32,000 mg / liter of NaCl; working pressure of 800 psig (5-516 KPa), at 25 ° C, pH 6.5; % recovery equal to 15 #, after 24 hours. 24. Process according to claim 1 or 2, in which the first osmosis section 01-1 contains 4 "loops" L1-L4, connected together in series, each fed by its own recirculation pump PR1-PR4; each "loop" in turn contains 3 pressure vessels, arranged in series and / or parallel within the "loop", each containing 3 spiral membrane cartridges. 25- Process according to claim 1 or 2, the permeate fraction Px leaving the last "loop" L4 of the first osmosis section 01-1 is recycled to the first "loop" L-1 and reprocessed. 26. Process according to claim 1 or 2, in which the second osmosis stage is carried out by applying a constant operating pressure, comprised between 40 and 70 bar. 27. Process according to claim 1 or 2, in which the concentrate Cx leaving the first osmosis section 01-1 is discarded and sent for disposal, together with that produced in ultrafiltration; the permeate Px obtained from the first reverse osmosis stage 01-1 is sent to a tank S3, from which it is then sent to the second osmosis section 01-2; the concentrate Cx leaving the second reverse osmosis stage 01-2 is recycled to the first reverse osmosis stage 01-2, and the permeate Px leaving the second reverse osmosis unit 01-2 is sent to a tank S4, from which then it is sent to the drain. Method according to claim 1 or 2, wherein the second osmosis unit 01-2 consists of 3 groups of membranes (or "loops"). each containing 2 pressure vessels, each in turn containing 3 spiral membrane cartridges. 29- Process according to claim 1, in which the treated landfill leachate contains NH4> 1200 ppm, and has a conductivity ≥ 10,000 pS / cm, and the permeate obtained at the end of the process has NH4 values ≤ 10 ppm and conductivity <100 pS / cm (micro Siemens / cm). 30. Plant for the treatment of landfill leachate comprising an ultrafiltration section and one or more osmosis sections, characterized in that it comprises at least one auxiliary pump inserted in series in the circuit of a single osmosis unit, interposed between two successive groups of osmosis membranes of the same osmosis unit, so as to achieve an increase in the pressure of the fluid circulating under pressure in said osmosis unit. 31. Plant according to claim 30. wherein said auxiliary pump is inserted in series between a first series and a second series of groups of auxiliary membranes or "loops", each consisting of two groups of membranes (or "loops"), in the first group operates at pressures of 30-50 bar and the second group at pressures of 50-120 bar. 32. Plant for the treatment of landfill leachate comprising an ultrafiltration section and one or more osmosis sections, characterized in that it comprises a device for heating the leachate placed before the ultrafiltration membranes. 33One of a PB auxiliary pump to achieve a pressure increase in a circuit of fluid circulating under pressure inside a single reverse osmosis unit, which is part of a landfill leachate purification plant comprising an ultrafiltration unit and at least one reverse osmosis unit.